It is well known that springs operating under stress tend progressively to acquire some degree of permanent set and this tendency increases with increase of operating temperature. This effect can thus present a serious problem in some cases. For example helical coil compression springs used in internal combustion engines as valve springs operate at elevated temperatures as high as 160.degree. C.
To overcome this problem, attempts have been made to stabilize springs intended for operation under stress at elevated temperatures by subjecting them to a "hot scragging" or heat stabilizing treatment. In this prior art treatment, the springs are deliberately heated and loaded, while hot, so as to cause them to relax or collapse. This procedure has been effective in reducing somewhat the tendency toward changes in physical properties during subsequent operation under stress at elevated temperatures. But, the manner in which such heat treatment process is carried out is important, and methods or techniques previously proposed have not been generally as satisfactory as may be desired.